Gardai said two masked men entered and one fired several shots at the victim, in his mid 20s. He was pronounced dead at the scene.

Detectives are trying to establish a motive for the gun attack in the city bar, also known as the Oasis, on Fassaugh Avenue, off the Navan Road.

"This was a definite hit, they were sure he was there and they were definite there would be no recovery," said a garda source. "He was shot a number of times up close."

The gunmen, who wore dark clothing, fled the scene on a motorbike in the direction of the city. No other customer was injured in the pub, which has been sealed off for a forensic examination.

The victim was known to gardai and was previously jailed for drug offences and assault.

In February 2008 the cocaine addict was sentenced to six years, with 18 months suspended, for storing almost 56,000 euro of cannabis resin in his home to clear drug debts as he was in fear of his life after receiving a bullet in the post.

While awaiting sentence, Cullen and a relative were arrested for assaulting a female garda, whom he kicked in a stomach. He was later jailed for three years, with the final 18 months suspended, to run consecutive to the six-year sentence.

It is understood he was an associate of gangland boss Eamon Dunne, known as The Don, who was shot dead in the nearby Fassaugh House Pub in April 2010.